linux-kernel - Re: [PATCH] fs: xfs: add NULL pointer check

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Message-ID: <32fad707-fdab-75a6-f7e5-d356a0b86983@opensource.wdc.com>
Date:   Mon, 28 Mar 2022 12:40:59 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     cgel.zte@...il.com, djwong@...nel.org
Cc:     linux-xfs@...r.kernel.org, dchinner@...hat.com,
        chandan.babu@...cle.com, bfoster@...hat.com,
        allison.henderson@...cle.com, lv.ruyi@....com.cn,
        linux-kernel@...r.kernel.org, Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] fs: xfs: add NULL pointer check

On 3/28/22 12:26, cgel.zte@...il.com wrote:
> From: Lv Ruyi <lv.ruyi@....com.cn>
> 
> kmem_zalloc() is a memory allocation function which can return NULL when
> some internal memory errors happen. It is safer to check NULL pointer.
> 
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Lv Ruyi <lv.ruyi@....com.cn>
> ---
>  fs/xfs/libxfs/xfs_attr_leaf.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index 014daa8c542d..e6694f49f563 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -1571,6 +1571,8 @@ xfs_attr3_leaf_compact(
>  	trace_xfs_attr_leaf_compact(args);
>  
>  	tmpbuffer = kmem_alloc(args->geo->blksize, 0);

See kmem_alloc() code: this function cannot fail (it retries the
allocation until success). So checking for NULL pointer does not make sense.

> +	if (!tmpbuffer)
> +		return;
>  	memcpy(tmpbuffer, bp->b_addr, args->geo->blksize);
>  	memset(bp->b_addr, 0, args->geo->blksize);
>  	leaf_src = (xfs_attr_leafblock_t *)tmpbuffer;
> @@ -2290,6 +2292,8 @@ xfs_attr3_leaf_unbalance(
>  		struct xfs_attr3_icleaf_hdr tmphdr;
>  
>  		tmp_leaf = kmem_zalloc(state->args->geo->blksize, 0);
> +		if (!tmp_leaf)
> +			return;
>  
>  		/*
>  		 * Copy the header into the temp leaf so that all the stuff


-- 
Damien Le Moal
Western Digital Research